fix: command palette pin/unpin toggle reads stale closure

[samueljklee]

Summary

The command palette "Pin/Unpin Session" command only ever pinned sessions — it never unpinned them.

Root Cause

The pin-session handler is registered inside a useEffect and captures pinnedSessionIds from the closure scope. Since pinnedSessionIds is React state and the effect does not re-run when it changes, the handler always sees the initial empty Set(). This means isPinned is always false, so the command always pins and never unpins.

This is a classic stale closure bug in React hooks.

Fix

- const isPinned = pinnedSessionIds.has(sessionIdRef.current);
+ const isPinned = cmdCtxRef.current.pinnedSessionIds.has(sessionIdRef.current);

Read from cmdCtxRef.current.pinnedSessionIds instead of the stale closure variable. The cmdCtxRef ref is already updated every render with the current pinned session IDs, so it always has the fresh value. This matches the existing pattern used for sessionIdRef.current on the adjacent line.